A Christmas tree installed on a producing well ordinarily must have two valves in it. One is used routinely, while the other is kept open, being incorporated as a backup valve. Through the two-valve arrangement, safety is assured should failure of the one customarily used occur. While the structure may incorporate two valves for safety, there is some sacrifice. The Christmas tree stands quite tall on incorporating two valves. This is particularly true in the instance where ball or plug valves are used. As will be appreciated, as the diameter of the pipe cooperative with the valve increases, the valve also must increase in diameter. This inevitably increases the size and weight of the valve structure, and, on coupling two valves serially, the structure can become quite large. As it increases in size, cost also increases. An increase in size also requires more expensive valve operator mechanisms. A valve operator mechanism of increased capacity is required to open and close larger valves.
The present invention provides an alternate approach to the construction of duplicate valve structures. This apparatus provides a much shorter valve body structure. The valve body is reduced in height through the use of flat disks. While the disk can be increased substantially in diameter, the thickness of the disk can remain fairly constant so that the valve body has a limited height, even for very large diameter pipe. Thickness of the disk is more nearly dependent on the pressure rating than the diameter of the valved line.
The present apparatus is less costly to manufacture. It incorporates a valve disk which is rotated. At the time of manufacture of the valve disk, it is constructed with a surrounding groove. It is not necessary to cut a gear on the outer surface. Rather, the gear is formed of a succession of ball bearings received in an outer groove and cooperative with a raceway in the valve body. The multiple bearings in succession thus function as a driven gear for rotating the disk. They are readily engaged with a drive motor and worm for opening or closing the disk within the valve body.
Cost of fabrication of the present apparatus is reduced through the utilization of a flat disk to support the valve element. It is easier to machine a round disk in comparison with a tapered plug or sphere. Machining of the valve body is also easier as a result of the shape of the valve disk. The use of a disk enhances pressure sealing to obtain a balance across the disk when the valve is open so that opening and closing of the valve is accomplished against reduced loading as a result of pressure differential. The pressure differential which occurs in this structure is used to energize the seat or seal supported within the flat disk. The seat or seal mechanism is received in a counterbored passage through the valve disk, the passage being constructed with counterbores for receiving the seat in it against bias springs which load the seat against the sealing surface.
Various alternate forms of the apparatus are disclosed. One alternate form incorporates seats which face in both directions to thereby accommodate flow in both directions. Another embodiment utilizes a flat valve disk supported on bearings which is rotated to serve as a safety cutoff valve in a mud flow choke. The choke is also formed in a flat valve disk. The choke is furnished with a throttled opening formed from a very hard metal such as tungsten carbide. The throttled portion of the passage is in the form of a replaceable insert. To the extent that the throttle is fairly long, the structure utilizes a pair of rotatable disks, and the insert is formed in two pieces. When the flat valve disk which supports the insert is aligned with the inlet and outlet opening through the valve, flow through the constricted choke insert occurs. When the choke wears badly and requires replacement, the flat valve disk is rotated to close the choke assembly to the flow of drilling mud. The flat valve disk is rotated so that the choke is no longer aligned with the flow between inlet and outlet of the assembly. Rather, the choke is then positioned adjacent to a removable plug in the body, the plug limiting access to the choke insert. The plug is removed, and the choke is removed through the plugged opening in the body for easy replacement.